1. Field of the Invention
The present invention relates to performance evaluation systems for centrifugal chillers that include fixed-speed turbocompressors.
This application is based on Japanese Patent Application No. 2010-170665, the content of which is incorporated herein by reference.
2. Description of Related Art
Recently, the need for performance evaluation of centrifugal chillers has been growing with the increasing social concern about reductions in energy consumption and CO2 emissions as countermeasures against global warming. In general, the performance of centrifugal chillers is evaluated using a measure called the coefficient of performance (COP) (see, for example, Japanese Unexamined Patent Application, Publication No. HEI-11-23113). The COP is calculated from the following formula, where a higher COP is evaluated as having a higher energy efficiency.COP=cooling capacity[kW]/power consumption[kW]
One possible method for allowing the user to accurately determine the performance of a centrifugal chiller is to show how high the current COP (hereinafter referred to as “measured COP”) is with respect to the maximum COP that can be achieved by the centrifugal chiller in terms of its performance (hereinafter referred to as “design COP”). In this case, because the design COP of the centrifugal chiller varies constantly with, for example, chilled water temperature, cooling water temperature, load factor, and the amount of refrigerant circulated, iterative calculation of the design COP is essential for showing the user how the measured COP compares with the design COP.
In the related art, however, the calculation of the design COP requires determining, for example, the performance of the heat exchanger and compressor constituting the centrifugal chiller and the thermal properties of the refrigerant from an enormous amount of operating data from the centrifugal chiller and inputting it to a dedicated program for carrying out a large number of convergent calculations. Accordingly, it is impractical to iteratively calculate the constantly varying design COP, and it is almost impossible to handle such calculation of the design COP in a refrigerator control panel which has a limited throughput.